Résumé
Understanding what limits plant growth under water deficit is an important issue because it could help in identifying target processes for the improvement of plant performance under drought. Primary metabolism, which provides energy and building blocks to biomass production, has been intensively studied in plants experiencing drought, but no clear picture has emerged so far. In particular, although it is well established that carbon fluxes are severely altered under drought, it is still unclear whether this would primarily affect plant performance. By using an integrative approach combining ecophysiology and multilevel metabolic phenotyping, we investigated growth and metabolism in Arabidopsis plants subjected to mild and severe water deficits for up to several weeks. The results show that under drought, rosette growth rates were more reduced than photosynthesis, leading to an improved carbon balance. K+ and organic acids were the main contributors to osmotic adjustment, and water shortage led to a global increase in the turnover of carbon rich compounds (starch, soluble sugars, organic acids and amino acids), suggesting that relatively more carbon was available at night. A more favorable carbon status at night was confirmed by a shift in the levels of transcripts encoding sugar responsive genes. In contrast, most enzyme activities under study showed only limited response to water stress. Taken together, these data suggest that in our conditions, carbon status did not limit growth, being adjusted to drought, but without requiring an in-depth reprogramming of central metabolism.